PROJECT SUMMARY The main objective of this application is to explore the biological potential of serum exosomal miRNA and protein as biomarkers of amyotrophic lateral sclerosis (ALS). It is critical to develop a reliable biomarker for disease progression that would enable us to monitor the effect of treatment and improve the success rate of drug development.The incomplete knowledge of ALS pathophysiology and the absence of reliable biomarkers are major gaps in our understanding of the disease. We previously identified a unique microRNA and immune gene expression signature in blood monocytes from ALS mice and ALS patients. microRNAs are uniquely enriched in exosomes, which are extracellular vesicles and have been isolated from biological fluids such as plasma and serum. Exosomal microRNA can provide insight into the state of the cell in which the exosomes are released. Exosomes not only carry miRNA but also pathogenic molecules of ALS, such as TDP-43 and SOD1. Thus, altered miRNA and protein in exosomes may result in the dysregulation of biological pathways that contribute to the development and/or progression of ALS. There is so far no systematic investigation of blood exosome miRNA and protein profiles before and after the onset of ALS. We hypothesize that abnormalities in miRNA and proteomic signatures in serum exosomes in ALS may serve as novel biomarkers for the prognosis and diagnosis of ALS. This study is supported by our highly unique longitudinal studies of subjects with sporadic (sALS) and familial ALS (fALS) and controls. In these studies, we collected serum samples over a four-year period at regular time points, while tracking disease progression clinically. Here, we propose a comprehensive profiling of miRNA and the proteins in serum exosomes. In Aim 1, we will identify serum exosome-based RNA and proteomic signature in sALS and fALS progression. In Aim 2, we will replicate and validate the identified biomarkers in another cohort of sALS and fALS. We believe that our findings, in combination with the clinical information collected at each time-point, will allow us to define an ALS miRNA and proteomic signature in serum exosomes and serve as a potential biomarker of ALS progression. !